The present invention relates to an optical lens having a lens element produced of plastic, more particularly plastic which is transparent in a visible spectral range, and having a coating comprising a plurality of layers, the plurality of layers comprising at least one high-refractive-index layer.
Used increasingly often nowadays as the material for optical lenses, especially in the case of spectacle lenses, instead of a silicate glass, is a plastic which is transparent in the visible spectral range. Relative to the silicate glass, the plastic affords the advantages of a lower weight, a greater breaking strength, colourability, and the possibility of attachment of a rimless frame. A known disadvantage of plastic optical lenses, however, is the much greater susceptibility of the surface to mechanical exposures, and particularly to damage by scratching.
In order to minimize this susceptibility to mechanical exposures of optical lenses made of plastic, a coating is applied to the plastic, and is intended to protect the optical lens from mechanical events. Generally speaking, this protective function is taken on by a hardcoat. The hardcoat must likewise be transparent in the visible range and must have a refractive index close to that of the optical lens, in order to ensure high optical transparency and to prevent unwanted colour interference. Typical materials for hardcoats are siloxane or an organically modified ceramics, which organically modified ceramics have a polysiloxane matrix, wherein a metal atom, for example titanium, is built into the polysiloxane matrix instead of an oxygen atom.
Additionally known is the provision of what are called anti-reflective layers on the optical lenses, for the purpose of preventing disruptive reflections. Usually, this is achieved by a sequence of layers, wherein layers having a first refractive index and layers having a second refractive index which is higher compared to the first refractive index are applied in an alternating manner. In the aforementioned document EP 0 698 798 A2, a proposal was already made to incorporate these anti-reflective layers, which are composed, for example, of inorganic, oxidic and optically transparent materials, into the design of the coating for protection against mechanical exposure.
Document EP 0 698 798 A2 proposes a coating comprising borosilicate glass applied to the lenses by means of a PVD (Physical Vapour Deposition) method. The coating is said to have a thickness of up to 3 μm as scratch protection. Although such a layer does protect the plastic lens from mechanical effects such as scratches, it does not prevent the possibility of the layers beneath or on this layer, intended for the provision of scratch protection, in other words, in particular, the anti-reflective layers, being scratched themselves and thus leading to hazy layers which scatter light.
It is an object of the present invention, therefore, to provide an optical lens, more particularly a spectacle lens, with a coating which as well as having good antireflection properties is insusceptible to mechanical exposures.